Locator calculation according to IARU:

Latitude and longitude from the IARU locator:

Description:

I didn't found any useful conversion between the common radio amateur's locator (IARU) and the geographic coordinate system. Nothing found, I took a deep breath and made a Java script by myself.
The IARU locator is not a fixed point on earth, the locator is a network of spherical four corners: In the longitudinal direction (from west to east) its 2' (two arc minutes) and 30" (thirty seconds of arc), in the latitude direction (north to south) its just 5' (five minutes of arc).

The locator has following structure:

JN76OT:

• JN ... fields (German language: Gr��tfelder), from AA to RR, i.e. 18 x 18 = 324 fields. These fields are divided into
• 76 ... squares (German language: Gro�felder), from 00 to 99, i.e. total 100 squares per fields. These squares are divided again into
• OT ... subsquares (German language: Kleinfelder), from AA to XX, with 24 x 24 = 576 subsquares per square.

In sum, the network consists of 324 x 100 x 576 = 18,662,400 subsquares.
At the equator, the expansion of a the small subsquare is 40,076.6 km / 4320 = 9.28 km in the longitudinal direction and (40,009.1 km / 2) / 4320 = 4.63 km in the latitude direction. Auf unserer Breite (47. degree of latitude, Vienna/Europe) the expansion in the longitudinal direction is only (40,076.6 km / 4320) x cos (47�) = 6.33 km; The expansion in the latitude direction of course remains the same everywhere (4.63 km). At North Cape (approx. 71 degree of latitude) the expansion in the latitude direction is only 3.02 km.

OM Tom, OE6TKT